1. In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.

2. In a large mixing bowl, beat softened butter with brown and granulated sugar until light and fluffy.

3. Add egg and vanilla extract and mix until fully combined.

4. Gradually add dry ingredients to wet, mixing just until incorporated.

5. Fold in chopped dark chocolate.

6. Cover dough and chill for at least 30 minutes.

7. Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.

8. Scoop 1.5 tablespoon portions of dough and space them 2 inches apart.

9. Bake for 10–12 minutes or until edges are set and centers are slightly soft.

10. Cool on the tray for 5 minutes, then transfer to a wire rack.

11. Once cooled, dip half of each cookie in melted chocolate.

12. Sprinkle with chopped roasted hazelnuts while chocolate is still wet.

13. Allow chocolate to set at room temperature or refrigerate for 15 minutes.